1. Field of the Invention
The present invention relates to an apparatus for displaying the residual capacity of a battery for use on an electric vehicle, and more particularly to an apparatus for displaying the residual capacity of a battery for energizing an electric motor to propel an electric vehicle, the fully charged capacity of the battery, and the temperature of the battery in a manner to be related to each other.
2. Description of the Related Art
Electric vehicles carry secondary batteries that are chargeable for reuse as a power supply for energizing motors for propelling the electric vehicles and various electric accessories.
On the electric vehicle, the residual capacity of the battery is detected, and data of the detected residual capacity are displayed in an analog representation by a pointer-type meter. Based on the displayed residual capacity, the driver estimates the distance that the electric vehicle can travel before the electric vehicle starts to run or while it is running.
Japanese laid-open patent publication No. 54-63328 discloses a technical concept of displaying the used capacity of a cell.
According to the above publication, a change in the voltage across a cell while it is being discharged is detected, and the energy discharged from the cell is calculated based on the detected voltage change. A display device comprises a linear array of light-emitting diodes. A number of successive light-emitting elements, which correspond to the discharged energy which is calculated, from one end of the array are energized to display the discharged energy. The user of the cell can estimate the residual capacity of the cell based on the displayed discharged energy.
The arrangement in which the data of the detected residual capacity is displayed in an analog manner by the pointer-type meter is disadvantageous in that the data may not correctly be displayed due to an error of the pointer-type meter.
The secondary batteries mounted on electric vehicles are degraded when they are repeatedly charged and discharged. The fully charged capacity of the batteries is lowered when the batteries are degraded. Since the rated capacity of a secondary battery varies depending on the temperature of the battery, it is difficult to estimate the residual capacity of the battery highly accurately from the energy discharged from the battery.
It has therefore been desirable to add the display of the fully charged capacity of a battery on an electric vehicle to the display of the residual capacity of the battery.